(a) Field of the Invention
The present invention relates to a hydrogenation catalyst for use in the preparation of gamma-butyrolactone (GBL) from maleic anhydride (MAn), a method for the preparation thereof, and a method for preparing gamma-butyrolactone using the catalyst. More particularly, it relates to a catalyst useful for hydrogenation in the preparation of gamma-butyrolactone from maleic anhydride and a method for preparing gamma-butyrolactone from maleic anhydride using the catalyst under the mild reaction conditions of low temperature, low pressure, and a low molar ratio of hydrogen/maleic anhydride with high selectivity, high yield, and long-term stability.
(b) Description of the Related Art
Gamma-butyrolactone is a synthetic intermediate of solvents such as pyrrolidone or N-methylpyrrolidone. It is also the raw material for the production of N-vinylpyrrolidone, polyvinylpyrrolidone, butanediol, tetrahydrofuran, pharmaceuticals, and rubber additives for use in petrochemicals and electronic industries.
As conventional methods for the preparation of gamma-butyrolactone, there are dehydrogenation of butanediol and direct hydrogenation of maleic anhydride. Recently, as methods for preparing gamma-butyrolactone by the vapor phase hydrogenation of maleic anhydride in the presence of a catalyst have been operated with a low cost, numerous catalysts and processes using them have been developed.
As catalysts for the vapor phase hydrogenation of maleic anhydride, those comprising copper as a main component are mostly used. For example, U.S. Pat. No. 3,065,713 proposed a Cu—Cr catalyst, but as selectivity and conversion rate into gamma-butyrolactone are low, it has problems of recovering and recycling a considerable amount of unreacted succinic anhydride. To solve such problems of Cu—Cr catalyst, U.S. Pat. No. 5,698,713 and European Patent No. 332,140 proposed a Cu—Zn—Cr catalyst and a Cu—Zn—Cr—Al catalyst, respectively, but they are still unsatisfactory in catalytic performance, long-term stability, and productivity of gamma-butyrolactone. In U.S. Pat. No. 5,536,849, high selectivity for gamma-butyrolactone was obtained using a catalyst comprising CuO—Cr2O3—SiO2 prepared by activating Cu, Cr, and Si, but as its long-term stability is low, it still needs improvement. Also, so as to solve the handling problems of chrome-containing waste catalysts and to improve their performance, U.K. No. 1,168,220 proposed a reduced Cu—Zn catalyst, but its effect on performance improvement is low as compared with Cu—Cr catalysts.
Further, U.S. Pat. No. 5,347,021 disclosed that gamma-butyrolactone was prepared using a catalyst comprising a Cu—Zn—Al oxide with comparatively high selectivity and yield and long-term stability, but it has drawbacks—it requires the regeneration of catalyst at a high temperature after the lapse of a certain time from the time the reaction is initiated, and thereafter, re-activation should be done frequently to maintain the activity of the catalyst. It was operated in a high molar ratio of not less than 200:1 of hydrogen to maleic anhydride, thus being not advisable in an economical aspect. U.S. Pat. No. 6,008,375 disclosed a catalyst comprising CuO-Al2O3— graphite that has high selectivity and yield for gamma-butyrolactone and long-term stability, but in order to apply the process to industrial-scale production, there are still required mild reaction conditions such as a low reaction temperature and low molar ratio of hydrogen with regard to reactants, and a high productivity.
As described above, the direct hydrogenation process of maleic anhydride has problems of frequent re-activation due to the cocking of catalysts, low selectivity, low conversion rate of catalysts due to the sintering of catalysts, and a short lifetime of catalysts. Further, in the industrial aspect, the vapor phase hydrogenation process of maleic anhydride has environmental problem because catalysts containing a chrome component are employed in a large quantity. In addition, the vapor phase hydrogenation process for preparing gamma-butyrolactone should be operated under conditions of an excessively high molar ratio of hydrogen to maleic anhydride, it has comparatively low productivity, and it needs improvement in view of selectivity and conversion rate into gamma-butyrolactone.
To solve such problems of the prior arts, it was provided a Cu—SiO2 catalyst by stabilizing nanosized copper oxide (CuO) precursor particles with a colloidal silica and described in the Korean Intellectual Property Office (Korean Patent Application No. 2000-42410; Laid-Open No. 2002-8600). However, pilot plant operation using such catalyst revealed that when it was operated with a low molar ratio of hydrogen to the reactants, the catalytic activity was sensitive to changes in conditions such as reaction temperature, pressure, etc., thereby complicating the operation conditions, and butanoic acid was excessively generated as a result of reaction making the purification of gamma-butyrolactone difficult in the purification process, thereby reducing purification efficiency.